Rhodopsin regeneration is rod photoreceptor membranes involves photoisomerization of a protonated complex between all-trans retinal (vitamin A aldehyde) and phosphatidylethanolamine. A fluid membraneous environment provided by the unsaturated acyl chains of phospholipid is essential for the regeneration reaction. A method is being developed for extraction and purification of protein kinase associated with rod membranes, an enzyme that phosphorylates rhodopsin with ATP.